Fuel pump assemblies are often placed in wings of aircraft, adjacent to, or inside, fuel tanks housed within the wing. A fuel pump assembly may act as a transfer pump, used to transfer fuel from one fuel tank to another, or as a boost pump, to feed fuel to the aircraft engines.
The placing of aircraft fuel pump assemblies inside aircraft fuel tanks results in a need to observe stringent safety precautions in order to avoid or mitigate the risk of ignitions and explosions.
It is also desirable that aircraft fuel pump assemblies are removable for maintenance.
Aircraft fuel pump assemblies are traditionally powered by electric motors of the asynchronous induction or brushed permanent-magnet type. Such motors do not require any electronic control elements. In such a system, a pump motor is supplied with a fixed frequency 400 Hz 3-phase alternating current (ac) or a direct current (dc) electrical supply. When electrical power is supplied the motor rotates and, in turn, causes pump rotation at approximately constant speed.
An example of such a system is shown in FIG. 1.
The fuel pump assembly of FIG. 1 is located in a wing of an aircraft and contained in a fuel flooded canister. The canister projects into a fuel tank, housed in the wing. The canister is secured and sealed to the inside of the fuel tank wall.
A pump and electric motor, connected to form the fuel pump assembly, are removably housed within the canister. The fuel pump assembly can be removed from its position in the canister by unbolting a cover plate, located on the outside of the fuel tank, accessible from the outside of the wing and withdrawing the pump and attached motor. Sliding valves and check valves automatically close off the inlet and outlet of the pump, thereby allowing removal of the pump assembly without the need to drain fuel from the fuel tank.
Improvements in high-power, solid state switching electronics has allowed more efficient motors of the brushless or switched reluctance type to be developed. Such motors may be powered by an electric supply provided by variable frequency generators running at a speed proportional to the aircraft running speed.
The switching electronics required for such an improved motor manage high currents and voltages and require cooling. Similarly, a converter for converting variable frequency ac to dc is often also provided with the electronics. The converter also requires cooling.
An example of a fuel pump assembly including an improved motor is shown in FIG. 2.
The fuel pump assembly of FIG. 2 is located in a wing of an aircraft, within a fuel flooded canister. The canister projects into a fuel tank housed in the wing. The canister is secured and sealed to the inside of the fuel tank wall.
The fuel pump assembly is formed by connecting a pump, an electric motor and an electronics unit.
In use, the fuel pump assembly acts to transfer fuel from the pump inlet to the outlet. The pump also acts to force a portion of the fuel through each of the electric motor and the electronics unit, thereby effecting cooling.
The fuel pump assembly is removably housed within the canister and can be removed from its position within the canister by unbolting a cover plate and withdrawing the fuel pump assembly as described in relation to the arrangement shown in FIG. 1.
The present invention seeks to provide an improved fuel tank assembly. Alternatively or additionally, the present invention seeks to provide a fuel tank assembly which mitigates or eliminates one or more of the disadvantages associated with the arrangements illustrated by FIG. 1 or by FIG. 2 of the attached drawings.